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Old 03-19-2015, 05:46 AM   #1
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Default Overcooling, odd problem! (Fixed...................................)

So...

99 miata, MSM radiator, fans/shroud installed but they never turn on. Small tube/fin intercooler blocking 1/2 the radiator, and the condenser still in place, Reroute that lets heater core water return to radiator (no more mixing manifold), 180*F thermostat from Autozone, 8.5/10 on the ducting, factory undertray not installed right now but will be/should be.

Surprise, it overcools.

65*F outside, 65mph, 145-150*F water temps

Then I put a 3/8" ID restrictor in the heater core hose

65*F outside, 65mph, 155-160*F water temps.

Then I 100% plugged the heater core hoses.

65*F outside, 65mph, 174-190*F water temps. Basically it heats up, and around 190 the thermostat opens all the way, huge slug of cold water hits motor, motor drops to 170's, wash, rinse, repeat.

Then sheet of cardboard blocking 1/2 of radiator, temps stable at 181 on highway. With A/C on or off.

I ordered a new Super Stant 195*F, will try that when it gets here.

Any ideas for having a working heater? I didn't think a 3/8" hole would let enough water through to overcool the engine at highway speeds! I guess I can try an even smaller hole, anyone know what works? I went from 5/8" to 3/8" and gained 10*F.

Last edited by patsmx5; 03-20-2015 at 01:35 AM.
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Old 03-19-2015, 11:58 AM   #2
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"Reroute that lets heater core water return to radiator (no more mixing manifold)"
Well duh.

Re-isntall "mixing manifold". Install a 4-port oil cooler t-stat on the outlet of the heater, and plumb it back into the water pump inlet ("mixing manifold"). Plumb it so when coolant exiting heater is hot, it is closed (so hot water doesn't re-enter engine). But if you use the heater, the water exiting the heater will be cool, and the oil cooler will allow flow back into the engine. Note that this works properly if main t-stat setpoint is higher than the oil t-stat.

This has been tested years ago by Shaikh.
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Old 03-19-2015, 12:08 PM   #3
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Quote:
Reroute that lets heater core water return to radiator (no more mixing manifold)
n00b.
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Old 03-19-2015, 12:25 PM   #4
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Old 03-19-2015, 12:26 PM   #5
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Oh fun, you made a Racer Reroute.
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Old 03-19-2015, 02:41 PM   #6
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Quote:
Originally Posted by JasonC SBB View Post
"Reroute that lets heater core water return to radiator (no more mixing manifold)"
Well duh.

Re-isntall "mixing manifold". Install a 4-port oil cooler t-stat on the outlet of the heater, and plumb it back into the water pump inlet ("mixing manifold"). Plumb it so when coolant exiting heater is hot, it is closed (so hot water doesn't re-enter engine). But if you use the heater, the water exiting the heater will be cool, and the oil cooler will allow flow back into the engine. Note that this works properly if main t-stat setpoint is higher than the oil t-stat.

This has been tested years ago by Shaikh.
I more or less did what you are recommending years ago too. Had a valve that was vacuum controlled, could switch heater core water paths with it. I took it off as I have no space in that area now, I have a big blower there now. Also I figured if it overcooled, I could just restrict the line accordingly to fix it. That part is proving to be a pain though!

What surprises me is that at highways speeds, the engine can get all the cooling it needs, and then some, flowing water through a 3/8" orifice! I would not have thought that.




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Originally Posted by Braineack View Post
n00b.
Haha


Quote:
Originally Posted by hornetball View Post
Mine isn't exactly their racer reroute. It's a traditional-thermostat-on-rear-of-head reroute with the exception that the heater core water goes back to radiator.

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Originally Posted by concealer404 View Post
Oh fun, you made a Racer Reroute.
See above.

Basically I have tested this exact setup with a smaller radiator and it wouldn't overcool, just slow to warm up. I don't want any of the cooling water going back to the mixing manifold as that's going to make the engine run hotter on the track/reduce potential cooling, and as I said doing a valve/thermostat is more complexity and I no longer have the room for it. So for now, I'm going to try running a smaller restrictor in the heater hose. I guess the purpose of this post was to show what I'm doing, and what does and doesn't work, and ask What size restrictor people run. I don't think I'm the first to do this, so was hopping someone knows what size restrictor works. I guess I'll figure it out and post when I do!
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Old 03-19-2015, 02:51 PM   #7
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All you did was the Racer Reroute with the thermostat on the back instead of the front.

The size restrictor that will work will depend entirely upon ambient temps and how hard you flog. There is no single size that will work under all circumstances.

There's this thing called a thermostat. It was invented many decades ago to solve this exact issue. But, of course, you have to use one and not defeat it with a bypass. LOL.
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Old 03-19-2015, 02:54 PM   #8
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Call it whatever you like. I have thermostat in the right place unlike theirs. Like you said in your thread you linked, theirs could make cooling even-ness worse! Mine won't do that.
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Old 03-19-2015, 05:12 PM   #9
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Doesn't matter if the thermostat is physically located between your *** cheeks, its relative position in the cooling system order is what is important.

Put the mixing manifold back in, and your problem will be pretty much solved.
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Old 03-19-2015, 06:07 PM   #10
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Quote:
Originally Posted by fooger03 View Post
....
Put the mixing manifold back in, and your problem will be pretty much solved.
Yes, we all know that will fix it.

I already know that having even a 3/8 in orifice worth of water bypassing the radiator (which is way less than the 5/8" heater hose that goes to the mixing manifold from the factory) bypasses enough water to not only completely cool the engine at highway speeds, it will even OVERCOOL it! That's a lot of cooling for a little 3/8" hole!

This is obviously a decent amount of cooling, and I'll loose it by hooking it back to the mixing manifold. So I'm not doing that, my goal is to have as much cooling as possible. I did the math years ago and thought I'd see a 20% increase in cooling capacity by doing, but real world testing is leading me to believe a 20% bump in cooling capacity may be an underestimation.

I think I can fix this with a smaller restrictor in the hose. Will try this tonight and report back. The way I see it, I need the restrictor to limit flow to the point that it cant' flow enough to keep the engine cool at highway speeds, so the thermostat will still function as it should. But it has to flow something, otherwise the heater won't work. Probably try a 1/4" hole next and see what that does.

Area 5/8" = .307 in^2
Area 3/8" = .110 in^2
Area 1/4" = .049 in^2

In rough numbers, going from 3/8 to 1/4 should cut the flow area in 1/2.
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Old 03-19-2015, 06:42 PM   #11
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You made a Hyper reroute.
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Old 03-19-2015, 06:45 PM   #12
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Where are those "How to Have a Bad Time on MiataTurbo" montages?
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Old 03-19-2015, 07:26 PM   #13
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Quote:
Originally Posted by Savington View Post
You made a Hyper reroute.
??? I don't know what he did to be honest, but I remember him not understanding how things worked.

I do understand how this works. I want to make my cooling system work better, that's why I'm posting about this. To get feedback, opinions, ideas, experience, math, etc. I posted data on what testing I've done. When I used to post here several years ago it was common to discuss ideas and look for ways to make our cars faster and more reliable. I hate to think that has changed.
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Old 03-19-2015, 07:44 PM   #14
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Quote:
Originally Posted by patsmx5 View Post
I already know that having even a 3/8 in orifice worth of water bypassing the radiator (which is way less than the 5/8" heater hose that goes to the mixing manifold from the factory) bypasses enough water to not only completely cool the engine at highway speeds, it will even OVERCOOL it! That's a lot of cooling for a little 3/8" hole!

This is obviously a decent amount of cooling, and I'll loose it by hooking it back to the mixing manifold.
You are grossly overestimating how much cooling is being wasted into the mixing manifold. Yes, when the thermostat is closed and all the work going into the water pump is being directed at that little 3/8" orifice, it ends up being a lot. But as soon as the thermostat opens, the deltaP (and flow) across your orifice drops substantially.
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Old 03-19-2015, 08:33 PM   #15
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You are grossly overestimating how much cooling is being wasted into the mixing manifold.....
No I'm not. I have actually measured this before.

I used to have a valve that allowed me to switch between water returning to mixing manifold (stock) vs to upper radiator hose. I posted the results of this test either here or m.net, not sure where. I tested it at idle by measure fan on times vs off times to calculate the % of fan on time for each setup, Returning to mixing manifold was around 20% more fan time. I also did test driving the car, and datalogged it, and the datalogs showed lower temps AND faster recovery when the fans turned on.
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Old 03-19-2015, 09:03 PM   #16
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That sure is a super scientific test there.

Why can't you see it's exactly the same as drilling a big honkin' hole in the thermostat? That is not working for you, right?

Install a valve in the mixing manifold. Close it in the summer, and open it in the winter. I still say it's a waste of money though, and the lack of circulation behind a closed thermostat is likely why you have giant slugs of cold water. Your cooling system is a out of control mess, in other words.
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Old 03-19-2015, 09:17 PM   #17
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Quote:
Originally Posted by patsmx5 View Post
No I'm not. I have actually measured this before.

I used to have a valve that allowed me to switch between water returning to mixing manifold (stock) vs to upper radiator hose. I posted the results of this test either here or m.net, not sure where. I tested it at idle by measure fan on times vs off times to calculate the % of fan on time for each setup, Returning to mixing manifold was around 20% more fan time. I also did test driving the car, and datalogged it, and the datalogs showed lower temps AND faster recovery when the fans turned on.
You don't understand how thermostats work. All of your testing is thrown 100% out of the window when the thermostat opens. Put your mixing manifold back on.
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Old 03-19-2015, 09:25 PM   #18
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Quote:
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That sure is a super scientific test there.

Why can't you see it's exactly the same as drilling a big honkin' hole in the thermostat? That is not working for you, right?

Install a valve in the mixing manifold. Close it in the summer, and open it in the winter. I still say it's a waste of money though, and the lack of circulation behind a closed thermostat is likely why you have giant slugs of cold water. Your cooling system is a out of control mess, in other words.
Yes it's the same as drilling a hole in thermostat, that is obvious.

I have literally done exactly what you said, a valve, and I have already stated that in this thread!



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You don't understand how thermostats work. All of your testing is thrown 100% out of the window when the thermostat opens. Put your mixing manifold back on.
Yeah I do understand how thermostats work.

Why don't you like my testing? I didn't even post enough detail to draw conclusions like that! FWIW, thermostat was in "open" position during testing of course. Besides it's physics/basic heat transfer.

I can't believe how against people on this forum are to even discussing doing something to possibly improve the cooling ability of the car.
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Old 03-19-2015, 09:30 PM   #19
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...and the lack of circulation behind a closed thermostat is likely why you have giant slugs of cold water. Your cooling system is a out of control mess, in other words.
Ok this part. I don't know about that, you could very well be right.

As I said though, blocking 1/2 the radiator FIXED the temperature swings. That of course doesn't' change the circulation of water in the engine with the thermostat closed. It would only change the temp of the water going into the motor.

This leads me to think the thermostat is simply opening too much in a narrow temperature window. So say if it cracks at 180, it's fully open at 185 for example. I read last night the Super Stant thermostat's have a wider range from crack to full-open, and it's supposed to solve this exact problem on cars that have upgraded cooling systems that are used a low loads.

Will have report back with real world experience tomorrow!
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Old 03-19-2015, 09:58 PM   #20
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A thermostat is not a switch, it is neither on nor off once at temperature. You see what a small opening does, so this has to be obvious. You poking holes in it's differential will cause it to be out of control. You may as well just remove it, run allofthe cooling.

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Yes it's the same as drilling a hole in thermostat, that is obvious.

I have literally done exactly what you said, a valve, and I have already stated that in this thread!
You misunderstand me, it cannot drain water past the thermostat. It is a simple on/off ball valve. You will need to adjust it daily.

You blocking half the radiator lowered the temperature differential across the entire setup, so the thermostat was able to balance the imbalance you introduced easier. The weather will do this, every day all the time.

I did a reroute for 50 something bucks, my heater will always work, and my car gets and holds a temperature yet doesn't overheat. Don't be different to be different, that's fricken dumb.
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